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Functional Description
The FL7701 is a basic PWM controller for buck
converter topology in Continuous Conduction Mode
(CCM) with intelligent PFC function using a digital
control algorithm. The FL7701 has an internal self-
biasing circuit that uses the high-voltage switching
device. The IC does not need an auxiliary powering
path to the VCC pin typical in flyback control ICs or PSR
product family.
When the input voltage applied to the HV pin is over
25 V to 500 V, the FL7701 maintains a 15.5 V DC
voltage at the VCC pin for stable operation. The FL7701
has UVLO block functions such that when the V CC
voltage rises higher than V CCST+, the internal UVLO
power for the IC, has voltage ripple as well as the
rectification voltage after bridge, changing voltage level
according to the VCC capacitor value. Using this kind of
voltage fluctuation on the VCC pin, the IC can detect
the time reference and create the internal ZCD signal.
For precise and reliable internal reference for input
voltage signal, the FL7701 uses a digital technique
(sigma/delta modulation) and creates a new internal
signal (DAC_OUT) that has the same phase as the
input voltage, as shown in Figure 5. This signal enters
the final comparator and is compared with current
information from the sensing resistor.
block releases and starts operation. Otherwise the VCC
goes down to the V CCST- and IC operation stops.
V bridge
Bridge Diode
Output Voltage
Normally, the hysteresis function provides stable
operation even if the input voltage is operating under
the very noisy or unstable circumstances.
Input Voltage
Peak
JFET Output
Voltage
t
The FL7701 has a smart internal digital block for
determining input condition: AC or DC. When an AC
VCC
V dd Charging Voltage
JFET Output Voltage
t
source with 50 Hz or 60 Hz is applied to the IC, the IC
automatically changes its internal reference signal,
which is similar to input signal, for creating high power
factor. Otherwise, once the DC source connects to the
ZCD
DAC_OUT
t
IC, the internal reference immediately changes to DC.
t
1. Soft-Start Function
The FL7701 has an internal soft-start function to reduce
inrush current at startup. When the IC starts operation
following an internal sequence, the internal reference
slowly increases for a pre-determined fixed time. After
this transient period, the internal reference goes to a
steady-state level. In this time, the IC continually tries to
find phase information from the VCC pin. If the IC
succeeds in getting phase information, it automatically
follows a similar shape reference made during the
transient times, 7 periods. If not, the IC has a DC
reference level.
V bridge
Figure 5. Internal PFC Function
3. Self-Biasing Function
The self-biasing function, using an HV device, can
supply enough operating current to the IC and
guarantee similar startup time across the whole input
voltage range (80 V~308 V AC ). However, self-biasing
has a weakness in high-voltage condition. Normally,
the HV device acts as constant current source, so the
internal HV device has power loss when high input
voltage connects to the HV pin. This power loss is
proportional to input voltage. To reduce this power
loss, one of the possible solutions is an additional
resistor between the input voltage source and the HV
pin, as shown in Figure 6.
I LED
T/2 = 1/(Input Frequency * 2)
Bridge
Diode
EMI filter
U1
7*(T/2)
Normal Operation
ADIM
HV
Figure 4. Soft Starting Function in AC Input Mode
RT
VCC
OUT
CS
GND
2. Internal PFC Function: How to Achieve
High Power Factor
The FL7701 has a simple, but smart, internal PFC
function that does not require additional detection pins
for detecting input phase information or an electrolytic
capacitor for supply voltage stabilization. For achieving
high PF, the FL7701 does not use the rectification
capacitor after the bridge diode. This is important
because the IC instead uses fluctuation in the signal on
the VCC pin. Basically, the VCC pin, which is supplies
? 2011 Fairchild Semiconductor Corporation
FL7701 ? Rev. 1.0.4
6
Figure 6. High-Voltage Application
www.fairchildsemi.com
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相关代理商/技术参数
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FL7730MY 功能描述:LED照明驱动器 Single Stage PFC PSR Off-line LED Driver RoHS:否 制造商:STMicroelectronics 输入电压:11.5 V to 23 V 工作频率: 最大电源电流:1.7 mA 输出电流: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:SO-16N
FL7730MY_F116 功能描述:LED照明驱动器 Single Stage PFC PSR Off-line LED Driver RoHS:否 制造商:STMicroelectronics 输入电压:11.5 V to 23 V 工作频率: 最大电源电流:1.7 mA 输出电流: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:SO-16N
FL7732 制造商:FAIRCHILD 制造商全称:Fairchild Semiconductor 功能描述:Single-Stage PFC Primary-Side-Regulation Offline LED Driver
FL7732M 功能描述:LED照明驱动器 Single-Stage PFC PSR Offline LED Driver RoHS:否 制造商:STMicroelectronics 输入电压:11.5 V to 23 V 工作频率: 最大电源电流:1.7 mA 输出电流: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:SO-16N
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